WEDNESDAY, March 26, 2014 (HealthDay News) -- Legalization of medical marijuana does not lead to increased crime, and may even be tied to lower rates of offenses such as assault and murder, a new study suggests.

The findings challenge claims by opponents that legalizing medical marijuana would lead to higher crime rates, the University of Texas at Dallas researchers said.

They analyzed crime rates in all 50 states between 1990 and 2006. During that time, 11 states legalized medical marijuana: Alaska, California, Colorado, Hawaii, Maine, Montana, Nevada, Oregon, Rhode Island, Vermont and Washington.

Using FBI data, the researchers looked at rates of murder, rape, assault, robbery, burglary, larceny and auto theft. None of these types of crimes increased in states that legalized medical marijuana, according to the study, which was published in the journal PLoS One.

"We're cautious about saying, 'Medical marijuana laws definitely reduce homicide.' That's not what we're saying," study author Robert Morris, an associate professor of criminology, said in a university news release.

"The main finding is that we found no increase in crime rates resulting from medical marijuana legalization," Morris said. "In fact, we found some evidence of decreasing rates of some types of violent crime -- namely homicide and assault."

Since 2006, 20 more states and Washington, D.C., have legalized medical marijuana.

"This new information, along with continued education of the public on the realities of the negative aspects of smoking marijuana -- which there are considerable negative attributes -- will make the dialogue between those opposed and in favor of legalization on more of an even playing field," Morris said.

"It takes away the subjective comments about the link between marijuana laws and crime so the dialogue can be more in tune with reality," he said.

The researchers said they plan to look at how the legalization of recreational marijuana use in Washington and Colorado affects crime rates in those states.